What size alternator (amp)?

[Doc Holiday]

Could I get some advice on what size alternator I will need to power the following? The car has 2 MSD 6AL's, 2 MSD 4 stage digital retard boxes, 2 holley blue pumps, and a single stage NOS big shot kit plate kit. I may put an electric waterpump on in the future as well. Currently the car has a 70 amp alternator. The ignitions are not a redundant setup, they are on at the same time. This is a rotary engine and rotarys have two ignition systems. Think of it as two distributors built under one cap. Each combustion chamber has two spark plugs, and each plug fires 10 degrees apart, thus requiring two seperate ignition systems. Any advice would be appreciated.

Here is a picture of the car.

[John_Heard]

Boy hard to say Doc, but I have a feeling that you're probably ok with the 70. I've got an 80 amp in my car feeding a few more electric gizmos and it is keeping up fine. Where you'll run into problems is when you fire those nitrous solenoids because of their amp draw. You might try and test fire the solenoids with everything else on in the car and see what the voltage drops down to.

With the battery in the trunk lots of things come into play that's going to affect if the 70 is big enough, wiring size, quality of grounds etc. all of which are going to have an impact on this. The only real way to know is to make some passes and find a way to measure what the voltage is doing going down the track. Maybe a voltmeter with a hi/low recording feature could be used in some way.

[CoMax Racing]

I used to run a big block chevy engine with 3 stages of nitrous and three fuel pumps. There were 10 solinoids in total plus a MSD 7al-2 ignition. I was running a 70 amp to start but I found my batteries were always running at lower voltages and really never charged fully. I went to a 100 amp alt and problems solved. I realize the 100 amp will take alot of HP to run but Denso makes a really nice small one wire alt that isn't to bad.

You could always run a alternator bypass circuit as well.

Just my 2 cents

[John_Heard]

Oops - just got to thinking, mine's a 100amp, for some reason I was thinking it was an 80.

[ytnova]

I use a powermaster 100amp one wire on the usual 7al box, 2 fans, electric water pump, four solenoids, 2 fuel pumps, etc. and I have had no problems yet, just make sure you start with a fully charged battery every time you go out that way the alt. isn't trying to play catch up. A good deep cyle battery or something like a optima would benifit you as well.

[xdamxincx]

what about factoring in running head lights ? i have a 100 amp alt and run 4 noids and thats 23 amps right there .i think i am going to do an amp search on all the electrical stuff i have in my car.

[a1elec]

somewhere i read that alternator draw wasnt that much h.p. i cant remember where. anyone know what a 100 amp would take in h.p.?

[dadnova]

News to me. It doesent take anything to spine my altinator by hand. Didn't think it took much HP to run it or that the 100 amp would take more then a 80 amp would.

Here to learn.

[sc racing]

I know a guy who owes a dyno and hes done a lot of testing and its such a small loss in hp it really doesny make a difference.

[John_Heard]

The guy that I use to repair / build alternators for me locally has a test stand with an 110VAC motor on to spin the alternator with a belt while he puts a load on it and measures the current output. That motor probably isn't over a 2hp electric motor. A high amp alternator you can hear it drag the motor down some but doesn't stall it. I'll have to look and see how big it is next time I'm there. It's certainly not a lot of hp to turn one.

[dadnova]

I feel the more AMPS the better give me a 200 amp I don't like hooking the car up to a charger all the time as others do. Last year we ran all night long one pass after another, sometimes we got over 20 passes a night and just put fuel in the car. Never a charger. Plus the MSD box gets plenty of juice.